Presently, messages sent between a computer system and a coupling facility require Input/Output channels as generally described in U.S. Pat. No. 5,452,455: Asynchronous command support for shared channels for a computer complex having multiple operating systems, assigned to International Business Machines Corporation (IBM). Within prior IBM mainframes, as exemplified by the S/390 systems and recent z Series mainframes (s/390 and z Series are trademarks of IBM), while these channels can be shared by multiple operating system images within the computer system, the channel can only be allocated to a single coupling facility. These IBM mainframes are considered the closest prior art and described below in some drawings. This needed invention departs from the prior art practice and provides a mechanism needed to allow a single physical message I/O channel to be shared by multiple host images, both operating systems and coupling facilities, within a computer system having multiple CECs.